1. Field of the Invention
The present invention relates to a flow reversal arrangement for a downhole water pump positioned within a coal bed methane well casing. More particularly, the present invention relates to a water flow reversing structure positioned at a pump flow outlet, along with associated conduits for conveying the reversed flow to an elevation within the well casing that is below the elevation of the pump.
2. Description of the Related Art
An important source of methane, a major constituent of natural gas, is subsurface coal seams that contain methane. Coal bed methane is a byproduct of the decomposition of organic material and is held to coal particulates by water that is present within the coal seam. However, in such subsurface coal seams the gas is not readily available because it is trapped in the seam by the water. Thus, to liberate the gas, wells are sunk and include submersible pumps positioned within well casings for removing the water from the coal seam to lower the water pressure and thereby liberate the gas. The gas passes into the well casing and is pumped to the surface, where it is collected at the surface after water has been extracted from the coal seam. Such wells are referred to as coal bed methane wells.
The water withdrawn from the coal seams is generally pumped to the surface by submersible pumps driven by electric motors that receive electrical power from the surface by means of an electric cable. The composition of the water contained in such coal seams can vary, but in general it is of low quality because it contains large quantities of dissolved mineral solids, including dissolved sodium and bicarbonate. As a result, the water has salinity levels that make it unsuitable for plants and for discharge onto soils, although it can be and has been used as drinking water for livestock. Consequently, when large volumes of subsurface water from coal seams are brought to the surface, a disposal problem is presented by the excess water that cannot otherwise be effectively and economically utilized. One way to minimize the disposal problem is to reinject the water back into the ground, such as into seams that previously had the methane gas liberated. Another way is to reinject the water into the ground at a different elevation from that from which the methane is being withdrawn.
There is therefore a need for a compact and simple flow reversal arrangement that can be contained within a coal bed methane well casing for injecting extracted coal bed seam water into lower strata.